There has been a continuous need for a constant-velocity coupling capable of transferring substantial amounts of torque between drive and driven members which rotate about misaligned axes. A particularly demanding application for such a coupling is described in U.S. Pat. No. 4,804,352, to Schmidt, owned by the assignee of the present application. The application involves the transfer of over 4,000 horsepower between shafts which may rotate at up to a 10.degree. misalignment angle in a so-called tilt rotor aircraft, i.e. an aircraft which is designed either to fly, or hover, in a helicopter-like mode or to fly in an airplane mode. While the links in the patented coupling are designed to operate in a non-couplings designed to transmit torque between shafts rotatable around misaligned axis. The link incorporates an elastomeric bearing assembly of a particular configuration which resists propagation of undesirable tensile stresses in the elastic layers when the link is tensioned to transfer torque from the drive member to the driven member while being capable of reacting transient reverse torque conditions that may occur.
A preferred link includes an elongate link body having apertures at opposite ends within which are provided inner bushing members adapted to be connected to the drive and driven members. Between each inner bushing member and link body there is provided a series of alternating layers of elastomeric material and relatively inelastic shims. In a major arcuate zone adjacent the terminal end of the link body, the elastomeric layers are bonded to the link body and to the inner member. A minor arcuate zone of like alternating layer is provided diametrically opposite the first mentioned zone and is separated therefrom by discontinuities in the elastomeric layers, preferably provided by cavities extending transversely between the inner bushing member and the like body in conjunction with splits in the inelastic shims. In this minor zone, an elastomer layer is intentionally left unbonded from a shim, from the outer surface of the inner mounting bushing, or from the inner concave surface of the link body so that slip joint is provided which extends between the discontinuities. A slight separation exists along the slip joint when the link body is tensioned to transfer torque in one direction but is engaged when the link is compressed to react reverse torque conditions. Preferably, the arcuate extent between the discontinuities in the minor bearing suction is less than about 180.degree. relative to the pivot axis of the inner bushing member. Among other advantages, this construction reduces the stiffness of the inner member to pivotal and cocking motion relative to the link body, and it reduces substantially tensile stresses among the elastomeric layers when the link is tensioned during transfer of torque in the normal operating direction. The reduction in tensile stresses in the elastomeric layers reduces the proclivities for cracking and, therefore, enhances the service life of the link assembly.